The field of this disclosure relates generally to systems and methods for data reading and/or image capture, and more particularly, to illumination systems particularly applicable to imaging data readers.
Data reading devices are used to read optical codes, acquire data, and capture a variety of images. Optical codes typically comprise a pattern of dark elements and light spaces. There are various types of optical codes, including one-dimensional codes, such as a Universal Product Code (“UPC”) and EAN/JAN codes, and stacked and two-dimensional codes, such as PDF417 and Maxicode codes.
Data reading devices are well known for reading UPC and other types of optical codes on packages, particularly in retail stores. One common data reader in such systems is an imaging reader that employs an imaging device or a sensor array, such as a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) device. Imaging readers can be configured to read both 1-D and 2-D optical codes, as well as other types of optical codes or symbols and images of other items. Though some imaging readers are capable of using ambient light illumination, an imaging reader typically utilizes a light source to illuminate the item being read to provide the required signal response in the imaging device. An imager-based reader utilizes a camera or an imager to generate electronic image data, typically in digital form, of an optical code. The image data is then processed to find and decode the optical code.
Imager-based types of readers, either single plane (e.g., in counter horizontal reader) or dual plane/bioptic style readers (e.g., readers with a horizontal window and a vertical window), are popular for high volume applications. These readers typically have bright illumination sources that are potentially distracting to the operator.
FIG. 1 shows a top view of a common problem with an illumination field for a scanner 20 whose exit angles are not well controlled. In this undesirable case, illumination/light sources 22 have a much wider range of angles over which they emit light. Some of the illumination light propagates in the desired general direction of an incoming object 16, represented by rays 30. Some portion of the light not emitted in the direction of the rays 30 may go in directions roughly orthogonal to the rays 30, represented by rays 32, 34. Some of the rays 32 may travel towards an operator 10 and some of the rays 34 may travel away from the operator 10 (potentially toward the customer).
FIG. 2 is an end view of the undesirable situation previously shown in FIG. 1. A work surface 24 and the scanner 20 are shown in cross-section. The light sources 22 produce light which is not well controlled in exit angle. Light from the lights sources 22 which travels in a desired direction toward the items being scanned is represented by rays 30. Some of the rays 32 which travel in an undesirable direction may enter the eyes 12 of the operator 10. Another set of rays 34 may similarly enter the eyes of customers (not shown) standing on the opposite side of the work surface 26. This “stray” light is not preferred and removing it would be beneficial.
FIG. 3 illustrates a scanner 50 that exhibits a common solution to the stray light problem. The scanner 50 is shown in cross-section and the work surface has been omitted. Only a single light source 52 is shown, and baffles 54, 56 are shown, but there may indeed be an array of light sources and baffles. The representative rays, labelled a, b, c, d, and e exit the scanner 50 through its window 51. It is noted that none of the illumination rays a, b, c, d, e enters the eyes 12 of the operator 10. The extent of the baffles 54, 56 is selected to block rays which would otherwise enter the eyes 12 of the operator 10. Additional baffles to control rays in the directions normal to this page may also be used, but are not shown here for clarity. The inner surfaces of the baffles 54, 56 are made with a light absorbing material, coating, etc. to reduce scatter of light impinging on the inner surfaces of the baffles. An unfortunate consequence of baffling the light sources is that the blocked light is entirely wasted, reducing overall efficiency of the illumination system.
FIG. 4 illustrates another example system of a scanner 60, but with the inner surfaces of baffles 64, 66 being made with reflective metal, or coated with highly reflective coating, such as a metallized layer. This reflective inner surface may be employed to improve the illumination efficiency. In this example, the light source 62 of the scanner 60 is surrounded by the metallized baffles 64, 66, and directs out light rays a, b, c, d, e but also shows that the stray light problem has reappeared. Some light, represented by ray f, reflects from the inner surface of one or more of the baffles 64, 66, exits window 61, and travels into the eyes 12 of the operator 10.
U.S. Pat. No. 9,305,198 at FIG. 19 discloses a system with a pyramid-shaped cone light concentrator with some of the inner surfaces being of high reflectivity (to concentrate the light) and other of the surfaces being low reflectivity (to minimize stray light.
Still, the present inventors have recognized that it is desirable to minimize bright light from the illumination sources of these readers from reaching or interfering with the sight lines of the operator or the customer while also avoiding unnecessary light losses.